1. Field of the Invention
The present invention relates to a semiconductor device and a method of producing the same, particularly, to a method of producing a dynamic RAM having a capacitor of a grooved structure.
2. Description of the Related Art
FIGS. 3A and 3B show a process of producing a semiconductor device in which the technical idea of the present invention is not employed. In the first step, a field oxide film 2 is selectively formed on the main surface of, for example, a p-type silicon substrate 1, as shown in FIG. 3A. Then, a CVD-SiO.sub.2 film is formed on the entire surface, followed by patterning the silicon dioxide film and subsequently etching the silicon substrate 1 using the patterned silicon dioxide film as a mask so as to form a groove 3. After formation of the groove 3, the patterned silicon dioxide film is removed, followed by forming a capacitor oxide film 5 to cover the surface of the silicon substrate within the groove 3, and the main surface of the silicon substrate 1. The capacitor oxide film 5 is formed in a thickness of about 200 .ANG.. Then, a polycrystalline silicon film 6, which is patterned later to form an electrode, is formed on the capacitor oxide film 5 in a thickness of about 4,000 .ANG./
In the next step, the polycrystalline silicon film 6 is selectively removed by reactive ion etching (RIE) to form a capacitor electrode 6a, as shown in FIG. 3B. The etching time in this step should be about 30% longer than required for removing a polycrystalline silicon film having a thickness of 4,000 .ANG. such that the polycrystalline silicon film 6 should not be left unremoved in the etched portion. Then, the capacitor oxide film 5 is removed in the region where a transfer transistor is to be formed so as to expose the silicon substrate 1 to the outside, followed by forming a gate oxide film 7 and a transfer gate electrode 8 on the exposed surface in succession. Further, a drain region 9 and a source region 10 each consisting of an n.sup.+ -type diffusion layer are formed in the silicon substrate 1 such that the transfer gate electrode 8 is sandwiched between these source and drain regions in the lateral direction.
In a dynamic RAM of the construction described above, it is desirable for the capacitor to have a capacitance as large as possible in order to prevent, for example, a soft error. However, it has become difficult recently to ensure a large capacitance in accordance with the progress in the degree of integration of the semiconductor elements.
In order to increase the capacitance of the capacitor, it is necessary to make the groove 3 deeper or to make the capacitor oxide film 5 thinner. What should be noted, however, is that new problems are brought about, if the groove 3 is made deeper. For example, washing is made difficult, if the groove is made deeper. Naturally, the depth of the groove is limited. A new problem is also brought about in the case of making the capacitor oxide film 5 thinner. To be more specific, the capacitor oxide film 5 below the polycrystalline silicon film 6 is also thinned in the region other than the capacitor region, with the result that, in the etching step for forming the capacitor electrode, the silicon substrate 1 which should not be etched is also etched partly in addition to the oxide film 5 so as to do damage to the semiconductor substrate. It follows that deterioration takes place in the characteristics of the transfer transistor formed on the silicon substrate 1.